Search arXiv⌕ Search

arXiv · 1002.1574

On the Probable Existence of an Abrupt Magnetization in the Upper Chromosphere of the Quiet Sun

Abstract

We report on a detailed radiative transfer modeling of the observed scattering polarization in the H-alpha line, which allows us to infer quantitative information on the magnetization of the quiet solar chromosphere. Our analysis suggests the presence of a magnetic complexity zone with a mean field strength > 30 G lying just below the sudden transition region to the coronal temperatures. The chromospheric plasma directly underneath is very weakly magnetized, with ~ 1 G. The possible existence of this abrupt change in the degree of magnetization of the upper chromosphere of the quiet Sun might have large significance for our understanding of chromospheric (and, therefore, coronal) heating.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Jiri Stepan, Javier Trujillo Bueno. 2010-02-08. On the Probable Existence of an Abrupt Magnetization in the Upper Chromosphere of the Quiet Sun. https://doi.org/10.1088/2041-8205%2F711%2F2%2Fl133

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

Confidently Wrong: Why Ignoring Binaries Biases IMF Inference at Large Sample Sizes

The stellar initial mass function (IMF) high-mass slope $α$ is routinely measured by fitting single-star models to photometric samples that contain unresolved binaries. This practice introduces a systematic negative bias on $α$ that is constant with sample size $N$. Posterior credible intervals shrink as $1/\sqrt{N}$, so at sufficiently large $N$ the bias exceeds the full 95% credible-interval width and the true value falls outside the credible interval - a regime we call "confidently wrong." Building on earlier studies of the bias magnitude, we quantify the sample size at which this bias exceeds the statistical uncertainty. We quantify this bias using two idealized observation operators: mass-addition ($m_{\mathrm{obs}}=m_1+m_2$), a formal upper bound on unresolved-system mass overestimation, and luminosity-addition ($m_{\mathrm{obs}}=L^{-1}(L_1+L_2)$), an idealized lower-bias photometric case based on the ZAMS mass-luminosity relation. Across four astrophysical environments spanning $α=1.60$-$2.30$, we find: (1) mass-addition bias of 0.054-0.086 with crossover to confidently wrong at $N_{\mathrm{cross}}\sim5{,}000$-$10{,}000$; (2) luminosity-addition bias of 0.011-0.021 with $N_{\mathrm{cross}}\sim75{,}000$-$150{,}000$; and (3) a binary-aware mixture likelihood that marginalizes over the Moe & Di Stefano (2017) binary population model recovers the true slope in the synthetic tests presented here. Published single-star IMF slopes can therefore plausibly carry systematic errors of order 0.01-0.09 if unresolved binaries are not modeled, comparable to or exceeding reported uncertainties in some regimes. Since current and upcoming surveys (Gaia, JWST, Roman, LSST) will deliver large resolved-star samples, binary-aware inference is likely necessary to avoid binary-driven systematic bias in the large-$N$ single-star-fitting regime.

astro-ph.SR↗

Finite-Element Asteroseismology I: Two-Dimensional Adiabatic Oscillations of Rapidly Rotating N=3 Polytropes

We develop a finite-element formulation for linear adiabatic oscillations of axisymmetric uniformly rotating, centrifugally distorted, self-gravitating N=3 polytropes. Equilibrium models are constructed using self-consistent-field iteration and then remeshed on a surface-fitted oblate meridional domain. The quadratic eigenvalue problem describing oscillations for each azimuthal wavenumber $m$ is solved using a conforming two-domain mesh. The density-weighted displacement, $\boldsymbol{u}=ρ^{1/2}\boldsymbolξ$, is defined in the stellar interior, whereas the gravitational-potential perturbation $δΦ$ is solved both inside the star and in an exterior vacuum. The coupled displacement--potential problem is assembled and solved within FEniCSx as a polynomial eigenvalue problem. Without rotation, the axisymmetric modes agree closely with an independent one-dimensional calculation. For finite rotation rates, several clean axisymmetric $p$-mode branches of the spheroidal star successfully reproduce the frequencies tabulated by Reese (2006). The relative frequency differences induced by rotation are smaller than $3\times10^{-4}$ for the low-order mode branches up to $\sim 60$\% of the critical rotation rate. These tests validate both the centrifugally distorted equilibrium and the finite-element implementation. We develop a method to track eigenfunctions continuously as a function of rotation and decompose their angular structure to quantify rotational mode mixing and progressive coupling between different spherical harmonic components. This reveals continuous deformation of individual mode branches from nearly single-$\ell$ structures to strongly mixed states at rapid rotation. This work is intended as a step toward finite-element multidimensional asteroseismology frameworks for modelling realistic rotationally and tidally distorted stellar configurations.

astro-ph.SR↗

An HST survey of photometry and multiplicity of brown dwarfs and planetary-mass objects in the field of Taurus

We present a photometric and multiplicity survey of 26 young objects with masses between 6 Mj and 37 Mj and spectral type later than M8 in the Taurus star-forming region with the Hubble Space Telescope. We search for companion candidates using two methods: a dedicated photometric technique based on the combination of colours from multi-band photometry and point spread function fitting. No companion candidates are detected beyond 30 au. With an updated membership and age identification, we determine luminosity, temperature, and mass for the 26 young objects using evolutionary models. We demonstrate that our HST observations are sensitive to companions down to masses of 1 Mj and even lower for some targets by artificial star injection tests. After survey completeness correction, we derive a binary frequency < 6.5% for this sample in the 68% confidence interval for companions with mass ratios between 0.1 and 1 and separations between 30 and 7,000 au. We find no significant difference in binary frequency among planetary-mass objects in Taurus, Upper Scorpius, and the field. These findings support that the binary frequency of planetary-mass objects is settled at young ages, probably younger than 1--10 Myr, suggesting that the formation of wide-orbit planetary-mass binaries is inefficient and the disruption of them likely occurs at a very early stage in a low density environment.

astro-ph.SR↗